Identification of an endemic Mediterranean brown trout mtDNA group within a highly perturbed aquatic system, the Llobregat River (NE Spain)

Abstract

Brown trout (Salmo trutta L.) is an important resource both for conservation and recreational fisheries in Iberian Peninsula, but the species is threatened in Llobregat River, an important river drainage in Catalonia (NE Spain), due to the high anthropological influence. In order to ascertain the native genetic diversity, phylogenetic relationships, population structure and stocking impact in this drainage, 295 individuals collected from eight different locations distributed throughout the main river course and the main tributary (i.e. Llobregat River and Cardener River, respectively) were analysed for the period 1990–2017. The complete mitochondrial DNA (mtDNA) control region and the LDH-C* diagnostic locus for monitoring the stocking were analysed. Moderate-high levels of genetic introgression were detected (frequency ~ 0.300), affecting especially the main course. Despite the stocking introgression and the expected genetic depletion by genetic drift due to population isolation, a new mtDNA haplotype group pertaining to the Mediterranean lineage was found restricted to the Cardener River. This haplogroup is responsible of the high population differentiation observed between rivers in the Llobregat drainage (ΦCT = 0.456, P < 0.001) and highlights the conservation interest of that region. Management strategies to achieve fisheries sustainability and conserve endemic resources in the region are proposed.